The present invention relates to adjustment mechanisms for movie cameras, particularly for mechanisms and methods for performing the timing function, that is the synchronization of the shutter movement to the film advance.
In movie cameras, film is moved behind a rotating shutter, the shutter selectively opening for a given period of time (i.e., exposure) and then closing, the film then moving to the next frame placing it in position for subsequent exposure. The exposure process is incrementally repeated.
It is very important that the film advance and the shutter be properly timed so that each film frame is stationary during exposure. Due to backlash or play between the related gears, pulleys, belts and the like, each camera needs to be individually timed to synchronize the shutter with the film advance mechanism.
A camera configuration is illustrated in FIG. 1. A motor 10 rotates a motor shaft 11 which through various gears and pulleys rotates the shutter 5 and the film advance mechanism (not shown). A helical drive gear 14 and a drive pulley 20 are mounted on a main drive shaft 12, the pulley 20 being coupled to and driven by the motor shaft 11. The helical drive gear 14 engages a helical driven gear 32 which is mounted upon a shutter drive shaft 30. On the opposite end of the shutter shaft 30 is mounted the shutter 5 which rotates therewith. The drive pulley 20 rotates a timing belt 22 which in turn rotates the driven pulley 24 which is mounted upon a drive shaft 26 which in turn supplies the driving force for the film advance mechanism. The shutter mechanism and the film advance mechanism both being driven off of the motor shaft 12 run at a synchronous speed. In order to obtain a proper timing due to play in the gear and/or belts, the angular position of the drive pulley 20 upon the main drive shaft 12 may be adjusted in order to properly time the film advance mechanism to the shutter 5. Once adjusted, the timing is set for that direction of rotation.
However due to special effects and other cinematographic techniques, it is desirable to film in reverse. The preferred reverse filming actually has the camera itself running in reverse. Due to the configuration of the gears and/or belts the amount of play in the reverse direction is different than that experienced in the forward direction so that the camera that is correctly timed in the forward direction is not correctly timed in the reverse direction.
To accommodate timing in the reverse direction, the camera can be run in reverse and the timing set by adjusting the rotational position of the drive pulley 20. However this timing adjustment must be done at the lab bench and is not conducive for adjustment in the field. Therefore if the director wishes to film a particular scene in reverse, he must either have a separate camera for filming the reverse filming scene or send his camera back to the lab to be timed for the reverse shots. Alternately, there are filming instances depending upon the film speed, exposure, or particular filming technique, where a small shutter angle may be set, the camera need not be adjusted between forward and reverse modes. However, depending upon filming conditions, especially at higher speeds, larger shutter angles and when using certain lighting techniques, it is very important to adjust the timing independently for both the forward and reverse modes.